Gas purification process



April 13, 1954 H. A. GOLLMAR 2,675,296

GAS PURIFICATION PROCESS Filed Nov. 25, 1948 T0 LIGHT 01L STILL PR1 MA RY COOLER v INVENTOR. H2s2r H Goa/'70P.

Patented Apr. 13, 1954 GAS PURIFICATION PROCES S Herbert A. Gollmar, Pittsburgh, Pa., assignor to Koppers Company, Inc., Pittsburgh, Pa., a corporation of Delaware Application November 23, 1948, Serial No. 61,688

Claims. I

The present invention relates to the liquid purification of Icy-product, coke-oven gas, and particularly to an improved process in which the coke-oven gas isscruhbed with an aqueous absorbent which is actified or regenerated by heating under subatmospheric pressure.

An object of the invention is to provide an improved process of the type described which provides for the separation and recovery of ammonia, hydrogen sulfide, and hydrogen cyanide.

A further object of the invention is to provide an improved process of the type described which can be carried out economically.

Another object of the invention is to provide an improved process of the type described which is arranged so that the heat required for the process is reduced to a minimum.

A further object of the invention is to provide an improved process of the type described which is arranged so that the heat required in actification or regeneration of the washing solution is supplied from a source of heat which is normally wasted, as, for example, by the liquor which is employed to cool the gas in the collecting main.

Another object of the invention is to provide an improved process of the type described which is arranged so that the subatmospheric conditions for the actification of the fouled absorbent are provided with a minimum of expense.

A further object of the invention is to provide an improved process of the type described which is arranged so that a vacuum pump of minimum size and operating cost is required to maintain the subatmospheric conditions in the chamber in which the fouled absorbent is actified.

Another object of the invention is to provide an improved process of the type described in which the gases given off during actification of the fouled solution are washed with ammoniacal the gas supplied to the vacuum pump to thereby eliminate formation of objectionable deposits'as a result of reactions initiated by the heat of compression of the gas passing through the vacuum pump.

Another object of the invention is to provide an improved process for removing ammonia from therefrom in a saturator. v

coke-oven gas and for forming ammonium sulfate A further object of the invention is to provide an improved process of the type described and in which the saturator is of relatively small size so that it can b constructed at low cost and so that it can be fabricated in a shop as a complete unit.

Another object of the invention is to provide an improved process of the type described which eliminates the necessity for passing the entire body of the coke-oven gas through the saturator and thus eliminates the attendant cost of compressing the gas.

A further object of the invention is to provide an improved process of the type described and in which the flushing liquor is employed as the ammoniacal liquid or secondary washing solution for washing the gas given off by the primary washing solution so that the supply of the secondary Washing solution to the ammonia still does not increase the load on the ammonia still.

Another object of the invention is to provide an improved process of the type described which includes means for supplying to the actifier from the flushing liquor water in an amount substantially equal in volume to that present in the gas leaving the actifier to thereby prevent any increase in the volume of liquid to be handled by the ammonia still.

A further object of this invention is to provide an improved process of the type described and which incorporates means to recover the naphthalene present in the gas and does so in such manner as to insure that the naphthalene will not interfere with the operation of the apparatus for carrying out the process.

Another object of th invention is to provide an improved process of the type described which eliminates the need for the final coolers which are usually employed in gas purification processes.

A further object of the invention is to provide an improved gas purification process of the type shown in U. S. Patent No. 1,654,782, issued Jan. 3, 1928, to E. H. Bird.

Other objects of the invention and features of novelty will be apparent from the following description taken in connection with the accompanying drawing, the single figure of which is an elevational view of apparatus for treating coke-oven gas with the process provided by this invention.

The apparatus shown in the drawing includes various units ordinarily employed in coke plants. Gases from a coke oven It pass through an ascension pipe H to the collecting main [2 which is provided with sprays M for spraying the gases with ammonlacal or flushing liquor which serves as a medium to cool the gases. The gas leaving the collecting main is at a temperature on the order of 75 C. (167 F.).

The tar and moisture condensed out of the gas collect in the bottom of the collecting main i2 and, together with the flushing liquor, flow through a downcomer l5 to a flushing liquor decantor or hot drain tank #6. A substantial portion, on the order of twenty percent, of the ammonia in the gas from the coke oven is ab=-- sorbed in the flushing liquor and remains in this liquor when this liquor flows from the collecting main to the decanter or drain tank 56.

The gas passes through the suction main I? to the primary cooler i8 which ispreferably of the:

indirect type in which the gas flows over tubes through which cooling water is circulated; Tar

and liquid condensing out of the gas in the primary' cooler flows to the tank 16 through a pipe Id." In the primary cooler the gases are cooled toa-temperatureon-the order of 35 C. (95 F).

The cooled gases are withdrawn from the pri'-- mary cooler it by the exhauster 2t and are pumped through the tar separator 2 i, from which condensates and collected liquids flow through pipe 22-to the tank l6; 7

In the-tank it the tar and ammonia liquor separate-into layers, and the ammonia liquor, which forms-the upper layer, passes from the tank l6 into a circulating tank 23" from whichit is pumped by a pump 25 and thence to the sprays 'llover a path hereinafter described. In

addition, as-herei'nafter explained, a portion of the ammonia liquor issupplied to the ammonia still and another portion is employed in the acti fication, orregeneration, of the solution which is employed towash the gas, while water vapor is taken from the-flushing liquor and added to the gases'given off during regeneration of the wash ing solution.

The cooledgas; free'from tar, is supplied from the'tarseparator 2| to the lower part of the upper section oftheabsorber 2bin which the gas is brought into contact with an aqueous alkaline primary absorbent solution, such as a solution. of sodium carbonate, which is pumpedby apump 28*frorn-the bottom of an actifier 39 through a lineti which hasa cooler 32 interposed therein; Coclingwater is supplied bysuitable means from any'appropriate-source to the cooler 32, and also to'the other coolers employed in this process. Theupper section of'the'absorber 2t ispreferably in the form of a packed tower through which the gas: is cooled by the washing. solution, and the.

various parts of the equipment are proportioned sorthatthe gas leaving the absorber is at a temperature-of about 25 C. (77 F.). The gas, substantially free of the constituents listed above, leaves'the absorber 26 through the outlet or discharge pipe 35a and may be subjected to any desiredjurther treatment for the. recovery of.

by-products present therein.

The acid-forming constituents in I The bottom of the upper section of the absorber 25 is conical and has a centrally located discharge pipe 29 which extends downwardly to a point adjacent the bottom of the lower section of the absorber. The pipe 29 extends through a plurality of horizontal baffies 33, alternate ones of which extend from opposite sides of the absorber. The baffles 33 are spaced apart vertical- 1y a short distance and cooperate to form a tortuousor circuitous path through which liquid flowing downwardly through the pipe 28 must pass'to reach the top-of the body of liquid in the lower section of the absorber.

Liquid tar from the tank It is pumped through pipe t l-by the pump. 35 to the upper part of the lower section of the absorber 25, while tar from the'bottom of the lower section of the absorber 2'6 is pumped by the pump 36 through the pipe 31' to the tank 18. Accordingly, there is a continuous downward flow of tar through the lower section of the absorber 26.

'I heprimary absorbent solution which collects inthebottom of the upper section of the absorber isrof lower specific gravity than the tar so it flows downwardly through the pipe 29 and thence'upwardly through the tar and forms a pool or layer of liquid on top of the tar.

The cool absorbent solution sprayed on the gas in the absorber 26- condenses naphthalene from the gas and this naphthalene is carried by the absorbent solution down-through the pipe 29 so that the naphthalene is discharged into the tar; The tar is an absorbent for the naphthalene, and because of the circuitous path through which the absorbent solution must travel in reaching the top of the tar, the naphth'alene is almost completely absorbed from the absorbent solution before the absorbent solution reaches the top ofthe tar. The naphthalene absorbedbythe'tar is carried by the tar to the tank It, and is removed from the tar during the refining of thetar by the methods customarily employed.

The pumps 35 and3'5'and the associated pipes may be governed in any suitable manner well known-in theart to'maintain the tar in the lower section of the absorber Ztat'a substantially constant level. 1

In addition, the-absorber 26 may have associated therewith means for preparing alkaline absorbent solution and for supplying solution to the circulating system for the absorber. This equipment has not been shown, but may be arranged substantially asshown in my Patent 2,464,805; granted March 27, 1949.

Fouled primary absorbent solution which col lects in thebottom section of the absorber- 2% is pumped therefrom through the pipe 38 by the pump 39 spraysdii in the-actifier 3B. The pipe 38 communicates with thelower section of the absorberZ'Sfat a point above'the level of the tar therein so that only washing solution is withdrawn through the pipe 38;

The actifier 3B is in the form of a packed tower and the nozzles 43 are located at an intermediate point in the tower. 1

The fouled primary absorbent solution in the actifier 30 is heated by the reboiler 4i mounted in. the base of the actifier and having coils.

through which relatively hot flushing liquor is circulated by the pump 25. The pressure in the actifier 30 ismaintained substantially below atsupplied from a sourceof heat which is normally wasted is adequate to cause the desired boiling or vaporizing of this solution. For example, the heat required in the actifier 30 may be supplied by circulating flushing liquor through the reboiler 4|, or itmay be supplied to'the actifier from any other source such as directly from the hot gas in the collecting main [2.

The flushing liquor is heated by the hot gas supplied from the ovens In to the collecting main I2. Hence, the flushing liquor circulated through the reboiler 4| in the actifier 30 provides means for transferring heat from the coke oven gas to the solution in the actifier. i i

As a result of the heating of. the primary absorbent solution and of the upward flow of vapors through the packingcountercurrent to the descendingprimary absorbent solution, the ammonia, hydrogen. sulfide and hydrogen cyanide.

present therein are largely expelled, and are carried out the top of the actifier together with the water which. is vaporized from the absorbent liquor. The regenerated primary solution which collects in the bottom of the actifier 30 is recirculated by the pump 28 and is returned through the cooler 32 to the absorber 26. The pump 28, or the pipe 3|, may be governed by appropriate means. to maintain .the liquid in the bottom of actifier3il at a suitable level.

.The gases emitted from the fouled primary absorbent solution in the actifier 31] leave the actifier through the pipe 42 and pass through the cooler .or dephlegmator 43 which condenses a major portion of the water present in these gases. The condensate from the dephlegmator 43 is pumped by a pump 44 through a pipe 45 to sprays 46 in the top of the actifier 30.

The flushing liquor leaving the reboiler 4i flows to a flash tank 50, the upper part of which is connected by a pipe 5| with the actifier 30 at an pressure so the space in the flash tank 50 above the level of the liquid therein is also below atmospheric pressure, and there is rapid evaporation of water from the surface of the relatively hot liquid in this tank. In addition, there is rapid.

escape of vapors, such as ammonia and hydrogen sulfide, from the liquid in the tank 50'. These vapors pass through the pipe 5| to the actifier 30 and add to the vapors therein.

:As stated above, the dephlegmator 43 cools the gases leaving. the actifier 3B and condenses a major portion of the water vaporthereirom, this condensate being returned to the actifier 30 through the sprays 46. However, the gas leaving the dephlegmator 43 contains some water vapor, audit the water represented by this water vapor were not returned to the system, the absorbent solution would soon be consumed.

Theflash tank 50 provides means for supplying moisture to the actifier 30 to compensate for the moisture taken from the actifier by the gas discharged therefrom. The surface area of the tank 53, the size of the pipe 5|,and the amount of cooling in dephlegmator 43 are selected and proportioned so that moisture supplied from the tank 50 to the actifier 30 is substantially equal in quantity to the moisture carried out of the actifier 30 by the gas leavingthe dephlegmator 43. Hence, the volumeoi the washing solution is not diminished by evaporation in the actifier.

. As hereinafterexplained, the water carried by thegas leaving the dephlegmator is supplied to li l-;..As; his vateristaken from the flushing liquor, there. is less flushing liquor: to be supplied to the ammonia still than would be the case if the water were supplied from a different source, and the total volume of liquid supplied to the ammonia still remains substantially unchanged.

As previously stated; the dephlegmator cools the gases leaving the actifier 36, while condensate from the gases is returned to the actifier. The cooling of the gases reduces their volume, which is helpful in maintaining the subatmospheric of 45 C. This efiects a substantial reduction in the volume of these gases without ohjectionably increasing the concentration of the absorbed gases in the condensate returned to the actifier. Liquid fromthe flash tank 5% is pumped by the pump 5? through pipe 53 to the sprays M in the,

collecting main !2, while a branch of the pipe 58 connects with the circulating system for the secondary absorber B0 and provides means for adding flushing liquor to the absorber 8G. The pump 51, or the pipes associated therewith, may be governed in any appropriate manner to maintain the liquid in the tank 50 at a substantially constant level.

Although most of the naphthalene is removed from the washing solution in the bottom of they vapor absorber 23, a small quantity of naphtha lene may be carried by the washing solution to the actifier 36 and be driven off with the gases leaving the actifier.

pipes and interfere with operation of the equipment, and means is provided to remove from the gas leaving the actifier any traces of naphthalene present therein.

The pipe 52 leading from the dephlegmator 43 is connected to the lower portion of a chamber 54 in which wash oil is sprayed by sprays 59.

The wash oil employed in these sprays may be the same as is employed in the recovery of light oils from coke-oven gas, while the oil which 001-.

lects in the bottom of the chamber 554 may be supplied to the stills forming part of the light oil recovery apparatus.

to the oil sprays andany traces of naphthalene present in the gas are absorbed by the oil. Hence, the gas leaving the chamber 54 is substantially free of naphthalene, while the naphthalene re- 1 moved from the gas is recovered during processing of the wash oil in the light oil stills.

61. The vapor absorber 60 is in the form of a packed tower in which the absorbent liquid and the gas both fiow downwardly. The pump 6! receives liquor from the bottom of the absorber A portion of the liquor discharged by the pump 1 6| is supplied over pipe to the ammonia still 10 .whilethis liquor is replaced by makeup liquor If permitted to remain in the gas, the naphthalene might solidify in the The gas in passing 1 through the chamber 54 moves in countercurrent;

supplied from, a branch: of 1 the pipe 53z'through which flushing iiquor' is; supplied to the'sprays I4: in the collecting main i2; Hence, the liquor supplied to the sprays 64- in the top oft-he vapor absorber 69" contains the makeup liquor and therefore has a substantially lower concentration of absorbed' gases than the liquor removed from the'bottom of the absorber by the pump 61.

It is to be understood that. the pumps 5-? and 61 may be regulated to controlthe pressures developed on the liquids discharge-d therefrom. It is to be understood also that the branch. of the pipe 58 leading to the cooler 62, and the pipes leading from: the: pump Ei'to the cooler 62 and to the still l'll have suitable control valves V and check. valves VCK therein to regulate the volume and. the direction of the flow of liquid there'- through. These valves may be arranged to perm'it flow of'liquid from the pipe 58 to the cooler 62' but'to. prevent flow of liquid from the pipe 58 to the pipe 55 leading .to the still it, and to also prevent flow of liquid from the pump 6| to the pipe 53.

The ammoniacal or flushing liquor with which the gas is contacted in the absorber 50 reduces the'volume' of the gas not only by cooling the gas and condensing water vapor present therein, but also by absorbing the constituents of. the gas. This liquor, when introduced into the absorber 60, has a relatively low concentration of ammonia, and, therefore, will readily absorb ammonia from the gas in the absorber. Similarly, this liquor, when introduced into the absorber 823, has a relatively low concentration of hydrogen sulfide and hydrogen cyanide so these are readily absorbed from thegas. The ammonia forms an alkaline compound when in solution, while the hydrogen sulfide andihydrogen cyanide have an acid reaction when in solution. Hence, the ammonia combines with the hydrogen sulfide and hydrogen. cyanide to form compounds which remain in solution and are removed with the liquor which is withdrawn from the bottom of the absorber 60 by the pump 6! and supplied to the ammonia still 16, which is of conventional construction and includes a free ammonia section, a, fixed ammonia section, and a lime leg. The

ammonia still 79 also includes a dcphlegmator through which passes the gas driven off from the liquor for supply to the ammonia still it, andthe rate of supply of replacement flushing liquor to the circulating system for the absorber ct are adjusted and proportioned so that at leasta large part of the ammonia, hydrogen sulfide, and

hydrogen cyanide present in the gas supplied to the absorber 60 are removed therefrom by the liquor. This absorption of gases by the liquor greatly reduces the volume of the gas discharged from the absorber 60.

Gas .discharged from the lower portion of the vapor absorber es flows through the pipe fifi to the knockdown tank 61 which also serves as a centrifugal separator for the removal of water entrained in the gas leaving the absorber 601-; The water removed from the gas in the tank 61 is returned by pipe 63 to the bottom of the absorber 60.

The gas discharged from the tank. '5"! is supplied to an acid washer H where the. gas passes through a sprayof: weaksulfuric acid which serves to remove traces of ammonia present in the gas. The gas discharged from the acid Washer H is supplied to the inlet side; of a vacuum pump '12, the exhaust side of which is connected by pipe 13- to the gas outlet Mof the saturator it; A pipe 76 leads-from the ammonia still '19 to the inlet'of the'saturator '15. The saturator 15 may he of any suitable construction well known in the art, as, for example, in PatentNo. 1,964,560, to Fred Denig, butbecause' of. therelativeiy'smail volume of the gas passing through the saturator, the saturator can be of much smaller size than would otherwise be necessary.

As explained above, the gas leaving the absorber 60 is washed with weak sulfuric acid before being supplied to the vacuum pump 12 so that all traces of ammonia are removed from the gas. This is advantageous because if ammonia is present in the gas supplied to the vacuum pump, the heat of compression will initiate reactions between the ammonia and othercon'stituents of the gas and will result in the formation of complex, gummy substances which will interfere with the operation of the vacuum pump and with other portions of the apparatus. The washing of the gas with weak sulfuric acid before' the gas is supplied to the vacuum pump removes the ammonia from the gas andeliminates this difficulty. The ammonia in the gas suppliedto. the acid washer ll combines with the sulfuric acid to form ammonium sulfate, while the acid with this sulfate in solution is supplied to the saturator it as part of the makeup acid therefore.

As previously stated, some of the liquor pumped by the pump 6! from the absorber SE! is supplied through pipe 55 to the ammonia still 10. This still operates in the usual manner. Steam for operating the still is supplied from a suitable source through a pipe 80, while spent liquor is removed from the bottom of the still through a pipe ti. As a result of heating in the still, the ammonia, hydrogen sulfide and hydrogen cyanide in the liquor supplied to the still are driven off, while contact of the liquor with the lime in the still decomposes the fixed ammonia compounds in the liquor so that the ammonia from these compounds is also driven off. i

The gas. from the ammonia still lfl'is supplied through the pipe "it to the saturator 15 where the gas passes through the weak sulfuric acid solution in the saturator 15 so that the ammonia in the gas is converted to ammonium sulfate which may be removed from the saturator in the usual manner.

The hydrogen sulfide and hydrogen cyanide present in the gas supplied to the saturator 15' pass through the sulfuric acid unchanged and are discharged through the pipe 14 to which the exhaust of the vacuum pump 12 is connected.

still i0 is taken from the absorber 60, but this does not represent an increasein the volume of liquor to be processed by the still 10 since the liquor taken from the absorber 6B is replaced by flushing liquor, thereby reducing the volume of flushing liquor supplied to the ammonia still.

Hence, the steam requirements of the ammonia still are not materially affected.

From the foregoing, it will be seen that the coke-oven gas, after cooling and after removal soi the tar therefrom, is supplied to the first or vapor absorber 60.

" primary absorber 26 where it is scrubbed subtion in the actifier is carried out under subatmospheric conditions so that heat which would otherwise be wasted is effective for this purpose. The pressure in the actifier 39 is on the order of 4.0 inches of mercury, absolute, so the solution in this absorber vaporizes readily when heated to the relatively low temperature to which it is heated by the flushing liquor circulated through the reboiler 4!.

This process is arranged so that the subatmospherio conditions in the actifier 30 are maintained with a vacuum pump of minimum size and minimum operating expense. The secondary vapor absorber 6B is interposed in the communication through which gas is supplied from the actifier 30 to the vacuum pump l2,,and the gas flowing from the actifier 3D to the vacuum pump is washed with a secondary absorbent solution in the form of coolammoniacal liquor inthe The volume of the gasis reduced not only by cooling the gas and con- ;densation .of water vapor present therein, but

is also greatly reduced by absorption of the gas in the washing solution and by chemical combination of the constituents of the gas with the ammonia in the washing solution.

The gas given off by the washing solution during its regeneration or actification in the actifier Si! is composed almost entirely of constituents which will be absorbed by the secondary washl elements from the gas. Accordingly, the volume of gas supplied to the vacuum pump 12 is relatively small and is much less than the volume of the gas given off by the absorbent solution being regenerated or actified in the actifier 30. As a result, only a comparatively small volume of gas mustbe handled by the vacuum pump 12 in order to maintain in the secondary absorber 60, and thus in the actifier 36, a relatively low pressure on the order of 4.0 inches of mercury, absolute. Hence, the vacuum pump 12 may be of relatively small size, and thecost of operation of this pump will be correspondingly small, thus making the process economically attractive.

The solution employed to wash the gas in the secondary vapor absorber is sent to the ammonia still where it is processed in the same manner that the flushing liquor is ordinarily treated. As result of this treatment of the solution from the absorber, the ammonia and other constituents are released from the solution so that the may be recovered in the usual manner.

The ammoniacal solution employed in the vapor absorber iii} is provided from the flushing liquor, and as the flushing liquor is normally sent to the ammonia still, the solution sent from the vapor absorber to the ammonia still does not increase the total amount of liquid sent to the 10 ammonia still, nor does it increase the heat required by the ammonia still.

In addition, water is extracted from the flushing liquor and is supplied to the actifier 38 in volume equivalent to water present in the gas leaving the actifier. This prevents reduction in the volume of the washing solution, and it also prevents an increase in the volume of liquid to be processed by the ammonia still. While this is the preferred arrangement, it is to be understood that the invention is not limited to this specific source of water vapor and that water vapor may be supplied from any other suitable source.

- Although it is preferred to employ flushing liquor as the ammoniacal solution in the vapor absorber 5!], the invention is not limited to this arrangement and it is contemplated that solution for the vapor absorber may be provided in other ways. For example, condensate from the dephlegmator which forms a part of the ammonia still may be employed as the solution in the absorber 60 instead of being returned directly to the ammonia still, or a special ammoniacal liquid may be-provided for the purpose.

Although I have herein illustrated and described in detail one form of gas purification process embodying my invention, it should be understood that the invention is not limited to these details and that numerous changes and modifications may be made Without departing from the spirit and scopeof the following claims.

Having thus described my invention, what I claim is:

1. A process for treating gas containing ammonia, and acidic gases for the separation and recovery of ammonia and acidic gases therefrom comprising: scrubbing the 'gas in a primary scrubbing step with an aqueous solution of an alkaline-reacting metal compound to absorb the acidic gases and ammonia, heating the fouled alkaline solution'in an actifying zone under subatmospheric pressure to drive off the absorbed acidic gases, ammonia and water while regenerating the absorbent solution, thereafter passing the acidic gases and ammonia under said subatmospheric pressure in a secondary scrubbing step into contact with a separate aqueous ammonia solution to absorb the acidic gases and ammonia un- "der said subatmospheric pressure, whereby the volume of gas is reduced sufficiently so that it can be practically handled in a vacuum pump distilling the rich aqueous ammonia solution to separate acidic gases and ammonia; therefrom,

in'which the acidic gases andammonia driven out of the alkaline absorbent solution are passed through a condenser to separate a major portion of the water therein before the gases are brought into contact with the ammoniasolution, and returning the condensed water to the alkaline absorbent solution.

2. A process for treating gas containing ammonia, and acidic gases for the separation and scrubbing step with an aqueous solution of an alkaline-reacting metal compound to absorb the acidic gases and ammonia, heating the fouled alkaline solution in an actifying one under subatmospheric pressure to drive off the absorbed ammonia therefrom, in which a vacuum is cre-. ated to draw vapors released from the alkaline absorbent in the actifying zone through the second scrubbing step, scrubbing any gases leaving the second scrubbing step with sulfuric acid, and then passing such gases through the vacuumcreating means.

7. A process of treating coke oven gas for the separation and recovery of ammonia, hydrogen sulfide and hydrogen cyanide comprising: collecting coke oven gas from a plurality ofcoke ovens in a main, scrubbing the gas passing through the main in a first scrubbing step, with an aqueous flushing liquor to cool the gas and absorb ammonia therefrom, thereafter passing the gas from the main through a body of an aqueous solution of an alkaline metal compound to remove hydrogen sulfide, hydrogen cyanide, and ammonia, heating the fouled alkaline absorbent solution under subatmospheric pressure L to drive ofiabsorbed hydrogen sulfide, hydrogen cyanide, ammonia and water while regenerating the absorbent solution, thereafter passing the acidic gases and ammonia in a second scrubbing step into contact with aqueous ammonia flushing liquor from the flushing main to absorb hydrogen sulfide, hydrogen cyanide and ammonia under said subatmospheric pressure, whereby the volume of gas is reduced sufficiently so that it can be practically handled in a vacuum pump to establish the required subatmospheric pressure in the said actifying zone, passing the thus treated gases through a vacuum pump todraw the vacuum necessary in said actifying zone, and distilling the so-formed rich ammonia liquor to separate hydrogen sulfide, hydrogen cyanide and ammonia therefrom, in which water is separated by condensation from the hydrogen sulfide, hydrogen cyanide and ammonia driven out of the alkaline absorbent solution before the hydrogen sulfide, hydrogen cyanide and ammonia are passed into contact with the ammonia liquor absorbent and the condensed water is returned to the alkaline absorbent solution in the absorbent zone.

8. A process of treating coke oven gas for the separation and recovery of ammonia, hydrogen sulfide and hydrogen cyanide comprising: collecting coke oven gas from a plurality of coke ovens in a main, scrubbing the gas passing through the main in a first scrubbing step with an aqueous flushing liquor to cool the gas and absorb ammonia therefrom, thereafter passing the gas from the main through a body of an aqueous solution of an alkaline metal compound to remove hydrogen sulfide, hydrogen cyanide, and ammonia, heating the fouled alkaline absorbent solution under subatmospheric pressure to drive off absorbed hydrogen sulfide, hydrogen cyanide, ammonia and water while regenerating the absorbent solution, thereafter passing the acidic gases and ammonia in a second scrubbing step into contact with aqueous ammonia flushing liquor from the flushing main to absorb hydrogen sulfide, hydrogen cyanide and ammonia under said subatmospheric pressure, whereby the volume of gas is reduced sufiiciently so that it can be practically handled in a vacuum pump to establish the required subatmospheric pres sure in the said actifying zone, passing the thus treated gases through a vacuum pump to draw the vacuum necessary in said actifying zone, and distilling the so-formed rich ammonia liquor to separate hydrogen sulfide, hydrogen cyanide and ammonia therefrom, in which acidic gases and ammonia are driven overhead from the ammonia distillation zone and then passed through sulfuric acid to absorb ammonia while separating the acidic gases from the ammonia.

9. The process defined in claim 7 in which water is evaporated from the flushing liquor and brought into contact with the alkaline solution absorbent in the actifying zone to supply an amount of Water to the absorbent solution substantially equal to the amount of water carried by the acidic gases and ammonia away from the condensing zone.

10. In a process for the recovery of ammonia, hydrogen sulfide and hydrogen cyanide from coke oven gases, the steps of cooling the hot coke oven gas, said cooling being effected in part by scrubbing said coke oven gas with flushing liquor whereby tar is condensed from said coke oven gas and ammonia is absorbed into said flushing liquor to provide a rich flushing liquor, separating the condensed tar from said rich flushing liquor, scrubbing the cooled coke oven gas with an aqueous alkaline absorbent solution to strip the ammonia, hydrogen sulfide and hydrogen cyanide therefrom in which scrubbing naphthalene is condensed and contaminates the rich absorbent, scrubbing the rich absorbent containing naphthalene with said condensed tar to scrub naphthalene therefrom, and thereafter regenerating ammonia, hydrogen sulfide and hydrogen cyanide from said rich absorbent.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,038,315 Doherty Sept. 10, 1912 1,654,782 Bird Jan. 3, 1928 1,822,380 Seil Sept. 8, 1931 1,971,798 Shoel Aug. 23, 1934 2,018,863 Miller Oct. 29, 1935 2,106,734 Gollmar Feb. 1, 1938 2,219,713 Schreiber Oct. 29, 1940 2,244,731 Schmalenbach June 10, 1941' 

1. A PROCESS FOR TREATING GAS CONTAINING AMMONIA, AND ACIDIC GASES FOR THE SEPARATION AND RECOVERY OF AMMONIA AND ACIDIC GASES THEREFROM COMPRISING: SCRUBBING THE GAS IN A PRIMARY SCRUBBING STEP WITH AN AQUEOUS SOLUTION OF AN ALKALINE-REACTING METAL COMPOUND TO ABSORB THE ACIDIC GASES AND AMMONIA, HEATING THE FOULED ALKALINE SOLUTION IN AN ACTIFYING ZONE UNDER SUBATMOSPHERIC PRESSURE TO DRIVE OFF THE ABSORBED ACIDIC GASES, AMMONIA AND WATER WHILE REGENERATING THE ABOSRBENT SOLUTION, THEREAFTER PASSING THE ACIDIC GASES AND AMMONIA UNDER SAID SUBATMOSPHERIC PRESSURE IN A SECONDARY SCRUBBING STEP INTO CONTACT WITH A SEPARATE AQUEOUS AMMONIA SOLUTION TO ABSORB THE ACIDIC GASES AND AMMONIA UNDER SAID SUBATMOSHPERIC PRESSURE, WHEREBY THE VOLUME OF GAS IS REDUCED SUFFICIENTLY SO THAT IT CAN BE PRACTICALLY HANDLED IN A VACUUM PUMP TO ESTABLISH THE REQUIRED SUBATMOSPHERIC PRESSURE IN THE SAID ACTIFING ZONE, PASSING THE THUS TREATED GASES THROUGH A VACUUM PUMP TO DRAW THE VACUUM NECESSARY IN SAID ACTIFYING ZONE, AND DISTILLING THE RICH AQUEOUS AMMONIA SOLUTION TO SEPARATE ACIDIC GASES AND AMMONIA THEREFROM, IN WHICH THE ACIDIC GASES AND AMMONIA DRIVEN OUT OF THE ALKALINE ABSORBENT SOLUTION ARE PASSED THROUGH A CONDENSER TO SEPARATE A MAJOR PORTION OF THE WATER THEREIN BEFORE THE GASES ARE BROUGHT INTO CONTACT WITH THE AMMONIA SOLUTION, AND RETURNING THE CONDENSED WATER TO THE ALKALINE ABSORBENT SOLUTION. 